Stephenson Harwood is being put on hold by first time client Nationwide over its plan to sue Barclays.
The firm had been fighting Nationwide's corner in a dispute over Barclays' proposed £1 charge to non-customers for use of its cashpoint, which the bank plans to introduce next month.
Nationwide gave Barclays until 23 September to back down.
Following an eleventh-hour meeting between the chief executives at each bank, Barclays has agreed to postpone its plan while Nationwide has put legal action on hold.
Nationwide claimed that Barclays breached the conditions of its Link network membership which allows customers of member banks and building societies to use other members' cashpoints.
It is the first time that Stephenson Harwood has acted for Nationwide. Its usual legal adviser Allen & Overy has been conflicted out of the case.
John Fordham, litigation partner at Stephenson Harwood, is acting for Nationwide with support from associate solicitor Victoria Whitesides.
However, Whitesides declines to comment on the proceedings.
A spokeswoman for Barclays says the “project” is being steered by the bank's in-house legal team, but Lovell White Durrant is providing legal advice on a consultative basis.
According to a spokesman for Nationwide, the company has used both Allen & Overy and Clifford Chance in the past but he says the bank likes to use a variety of firms.
He adds: “The plan was to get a high flyer in litigation with a good track record.”